The term prematurity conveys the impression of a shortened gestation, low birth weight, and the probability of some subsequent abnormality. Previous studies have shown that infants born prematurely tend to have slower development rates early in life and may even tend to be impaired on measures of intelligence, but there is no conclusive evidence as to whether prematurity is associated with an impairment relative to reproductive development. The present study examines the effects of premature and delayed delivery on the growth and reproductive development of the offspring, using a rat model system. Animals are cesarean delivered on days 22 (premature, 23 (normal), and 24 (postmature) of pregnancy and given to foster mothers. Progesterone treatment to certain mothers is initiated from day 20 to insure prolongation of pregnancy to day 24. The weight and histological maturity of organs in relation to birth weight and gestational age is examined in certain animals sacrificed at devlivery. Rats are weighed every other day, vaginal opening and estrus cycles recorded, and animals autopsied at 70 days of age. The critical period for androgen sterilization is also being analyzed relative to birth date.